Microbial nucleic acids represent a group of microbe-associated molecular patterns that are recognized through intracellular innate sensors triggering inflammatory responses. Toll like receptor 9 (TLR9) is the major receptor for microbial DNA. Using a reverse translational approach, we revealed that TLR9 contributes to periodontal disease pathogenesis through exacerbating the local inflammatory responses. Current proposal will extend our previous studies to fully characterize the biological pathways and cellular sources of TLR9-triggered inflammation in periodontitis. We will determine both the non-redundant as well as cooperative role of TLR9 with other innate sensors implicated in periodontitis. The effect of TLR9 inhibitors to periodontal disease outcome will also be evaluated. Periodontal disease is not only limited to gingival tissues but also is associated with various systemic diseases. Identification of periodontal microbial DNA at distant sites suggests that microbial nucleic acid sensing may not be only important in periodontal disease pathogenesis but also contributes to periodontal disease adverse effects on systemic health. Therefore, the proposed studies will not only identify novel biological pathways and therapeutic targets to control local persistent periodontal inflammation but also lead to future investigations to identify a novel link between periodontitis and systemic complications.